<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body {
            margin: 120px;
        }

        .circle-breath {
            background: pink;
            box-shadow: 0 0 0 0 rgb(204, 73, 152);
            height: 36px;
            width: 36px;
            border-radius: 50%;
            animation: donghua 2.4s infinite;
        }

        @keyframes donghua {
            0% {
                transform: scale(0.60);
                /* 注意rgba中的a的设置 */
                box-shadow: 0 0 0 0 rgba(204, 73, 152, 60%);
            }

            60% {
                transform: scale(1);
                box-shadow: 0 0 0 36px rgba(204, 73, 152, 0%);
            }

            100% {
                transform: scale(0.60);
                box-shadow: 0 0 0 0 rgba(204, 73, 152, 0%);
            }
        }
    </style>
</head>

<body>
    <div class="circle-breath"></div>
    <!-- 
        动画中应用背景色阴影，背景色阴影初始透明度为60%，后续为0
        搭配使用scale进行缩放，便可以达到圆圈呼吸扩散效果
     -->
</body>

</html>